Question

Indicate the type of isomerism exhibited by the following complex: $[Co(en)_3]Cl_3$

Hint:

Complexes of the type $[M(aa)_3]$ and cis-$[M(aa)_2b_2]$ are usually chiral and show optical isomerism. Trans forms of $[M(aa)_2b_2]$ are generally optically inactive due to symmetry.

Answer 1

Step 1: Understanding the given complex.
The complex given is \([Co(en)_3]Cl_3\), where "en" refers to ethylenediamine (a bidentate ligand), and the complex consists of a cobalt (Co) ion surrounded by three ethylenediamine molecules and three chloride ions as counterions.

Step 2: Identifying the isomerism.
This complex exhibits optical isomerism. Optical isomerism occurs when a complex has non-superimposable mirror images, just like how your left and right hands are mirror images but cannot be superimposed onto each other.
- The ethylenediamine ligands are bidentate, meaning they form two bonds to the central metal, creating a chelate ring.
- Since the complex has three such chelate rings, it can exhibit a form where the ligands are arranged in such a way that it has non-superimposable mirror images (enantiomers). These enantiomers are a result of the asymmetric arrangement of the ligands around the central metal atom.

Step 3: Other types of isomerism.
- Geometrical isomerism (cis-trans isomerism) is not observed in this case because all the ligands are identical (en ligands).
- Ionization isomerism or linkage isomerism do not apply in this case either, as the complex doesn't have any ambidentate ligands or exchangeable counterions that could lead to different ionization products.

Step 4: Conclusion.
The complex \([Co(en)_3]Cl_3\) exhibits optical isomerism due to the non-superimposable mirror image arrangement of the bidentate ethylenediamine ligands around the central cobalt ion.

Final Answer: The complex \([Co(en)_3]Cl_3\) exhibits optical isomerism.